Power conversion apparatus

ABSTRACT

A power conversion apparatus including a transformer, a power switch, a pulse width modulation (PWM) signal generator, an energy storage element, and a power circuit is provided. A primary winding of the transformer receives an input voltage from an external power source. An auxiliary winding of the transformer provides an auxiliary voltage. The power switch is coupled to the primary winding. The PWM signal generator generates a PWM signal to control on and off the power switch. The energy storage element is coupled to a power terminal of the PWM signal generator. The power circuit supplies power to the PWM signal generator and charges the energy storage element according to the auxiliary voltage. When a voltage of the energy storage element is greater than or equal to a threshold voltage, the power circuit stores backup power according to the auxiliary voltage. When the external power source stops providing the input voltage, the power circuit supplies power to the PWM signal generator and charges the energy storage element according to the backup power.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of and claims the priority benefit ofU.S. application Ser. No. 16/677,668, filed on Nov. 8, 2019, whichclaims the priority benefit of Taiwan patent application serial no.108115011, filed on Apr. 30, 2019. The entirety of each of theabove-mentioned patent applications is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND Technical Field

The disclosure relates to a power conversion apparatus. Specifically,the disclosure relates to a power conversion apparatus capable ofextending a hold-up time length of the power conversion apparatus.

Description of Related Art

In a power conversion apparatus, an input voltage provided by anexternal power source could be rectified to a DC voltage suitable formany kinds of electronic apparatuses. Therefore, power converters arewidely used in electronic apparatuses, such as computers, officeautomation equipment, industrial control equipment, and communicationequipment.

In a power conversion apparatus based on the pulse width modulation(PWM) control, the primary side of the power conversion apparatusgenerally has a power switch and a PWM control chip. The PWM controlchip is configured to control on and off of the power switch, so thatthe transformer in the power conversion apparatus may transferelectrical energy stored by the primary side to the secondary side ofthe power conversion apparatus and outputs the DC voltage to theelectronic apparatus. In addition, the auxiliary winding of thetransformer may provide power required by the PWM control chip foroperation through the power terminal of the PWM control chip. Further, avoltage regulator capacitor is generally disposed at the power terminalof the PWM control chip.

Generally, after the power source of the power conversion apparatus iscut, the power conversion apparatus is required to continuously outputthe DC voltage to the electronic apparatus during a period of hold-uptime, so as to lower the influence on the electronic apparatus caused bythe sudden power off. Nevertheless, since the capacitance of the voltageregulator capacitor of the PWM control chip is usually small, when thepower conversion apparatus is powered off suddenly, the PWM control chipis powered off as well and thus stops controlling on and off of thepower switch. As such, the power conversion apparatus stops outputtingthe DC voltage in a significantly short period of time. Therefore, theinsufficient hold-up time problem occurs in most of the existing powerconversion apparatuses, and as such, operational stability of electronicapparatuses is lowered.

SUMMARY

Accordingly, the disclosure provides a power conversion apparatuscapable of supplying power to a pulse width modulation (PWM) signalgenerator according to backup power stored by the power conversionapparatus when the power conversion apparatus is powered off, so as toextend the period of the hold-up time that the power conversionapparatus continuously provides an output voltage.

A power conversion apparatus in an embodiment of the disclosure includesa transformer, a first power switch, a PWM signal generator, an energystorage element, and a power circuit. The transformer has a primarywinding and an auxiliary winding. The primary winding is configured toreceives an input voltage from an external power source. The auxiliarywinding is configured to provide an auxiliary voltage. The first powerswitch is coupled to the primary winding and is controlled by a PWMsignal. The PWM signal generator is coupled to the first power switchand is configured to generate the PWM signal to control on and off ofthe first power switch. The energy storage element is coupled to a powerterminal of the PWM signal generator. The power circuit is coupled tothe auxiliary winding, the power terminal of the PWM signal generator,and the energy storage element and is configured to supply power to thePWM signal generator and charge the energy storage element according tothe auxiliary voltage. When a voltage of the energy storage element isgreater than or equal to a threshold voltage, the power circuit storesbackup power according to the auxiliary voltage. When the external powersource stops providing the input voltage, the power circuit suppliespower to the PWM signal generator and charges the energy storage elementaccording to the backup power.

In view of the above, the power conversion apparatus provided by thedisclosure may supply power to the PWM signal generator according to thestored backup power when the power conversion apparatus is powered off.In this way, after the power conversion apparatus is powered off, thehold-up time that the power conversion apparatus continuously providesan output voltage is extended.

To make the aforementioned more comprehensible, several embodimentsaccompanied with drawings are described in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate exemplaryembodiments of the disclosure and, together with the description, serveto explain the principles of the disclosure.

FIG. 1 is a schematic block diagram of circuits of a power conversionapparatus according to an embodiment of the disclosure.

FIG. 2 is a schematic block diagram of a power circuit according to anembodiment of the disclosure.

FIG. 3 is a schematic diagram illustrating circuit architectures of acharging circuit and a power backup circuit according to an embodimentof the disclosure.

FIG. 4 is a schematic diagram illustrating circuit architectures of acharging circuit and a power backup circuit according to anotherembodiment of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

In order to make the disclosure more comprehensible, several embodimentsare described below as examples of implementation of the disclosure.Moreover, wherever possible, elements/components/steps with the samereference numerals are used to represent the same or similar parts inthe drawings and embodiments.

FIG. 1 is a schematic block diagram of circuits of a power conversionapparatus 100 according to an embodiment of the disclosure. Withreference to FIG. 1, the power conversion apparatus 100 may include atransformer TR, a power switch Q1, a pulse width modulation (PWM) signalgenerator 120, an energy storage element 140, and a power circuit 160,which should however not be construed as a limitation in the disclosure.In an embodiment of the disclosure, the power conversion apparatus 100may further include an input capacitor CIN and a rectification circuit180.

The transformer TR has a primary winding Np, a secondary winding Ns, andan auxiliary winding Na. The primary winding Np is configured toreceives an input voltage VIN from an external power source. Thesecondary winding Ns is coupled to the rectification circuit 180 and isconfigured to provide an output voltage VO to a load. The auxiliarywinding Na is configured to provide an auxiliary voltage VA.

The input capacitor CIN is coupled between a first terminal (e.g., acommon-polarity terminal, i.e., a dotted terminal) of the primarywinding Np and a ground terminal GND1. When the external power sourcesupplies the input voltage VIN to the power conversion apparatus 100,the input capacitor CIN may store electrical energy. When the externalpower source stops supplying the input voltage VIN to the powerconversion apparatus 100, the electrical energy stored by the inputcapacitor CIN may release energy to the secondary winding Ns.

The power switch Q1 is coupled between a second terminal (e.g., anopposite-polarity terminal, i.e., a non-dotted terminal) of the primarywinding Np and the ground terminal GND1 and is controlled by a PWMsignal SP. The PWM signal generator 120 is coupled to the first powerswitch Q1 and is configured to generate the PWM signal SP to control onand off of the first power switch Q1. As such, the transformer TR maytransfer the electrical energy stored by the primary winding Np to thesecondary winding Ns and provides the output voltage VO to the loadthrough the rectification circuit 180. In an embodiment of thedisclosure, the PWM signal generator 120 may be implemented by adoptinga hardware circuit such as a micro-controller, an application-specificintegrated circuit (ASIC), a programmable logic device (PLD), or a fieldprogrammable gate array (FPGA), but is not limited thereto.

The energy storage element 140 is coupled between a power terminal PVCCof the PWM signal generator 120 and the ground terminal GND1 and isconfigured to stabilize a voltage of the power terminal PVCC. In anembodiment of the disclosure, the energy storage element 140 may beimplemented by adopting a capacitor, but is not limited thereto.

The power circuit 160 is coupled to the auxiliary winding Na, the powerterminal PVCC of the PWM signal generator 120, and the energy storageelement 140. The power circuit 160 may supply power to the PWM signalgenerator 120 and charge the energy storage element 140 according to theauxiliary voltage VA.

In particular, when a voltage VCC of the energy storage element 140(i.e., the voltage of the power terminal PVCC of the PWM signalgenerator 120) is charged to be greater than or equal to a thresholdvoltage VT, the power circuit 160 may store backup power EE according tothe auxiliary voltage VA. In addition, when the external power sourcestops supplying the input voltage VIN to the power conversion apparatus100, the power circuit 160 may supply power to the PWM signal generator120 and charge the energy storage element 140 according to the backuppower EE. In this way, if the external power source stops supplyingpower to the power conversion apparatus 100, the backup power EE storedby the power circuit 160 may prolong the time for powering the PWMsignal generator 120, so that hold-up time that the power conversionapparatus 100 continuously supplies the output voltage VO is therebyextended.

In an embodiment of the disclosure, the PWM signal generator 120 maydetect the voltage VCC of the energy storage element 140 through thepower terminal PVCC. When the voltage VCC of the energy storage element140 is greater than or equal to the threshold voltage VT, the PWM signalgenerator 120 may output a control signal group CSG to the power circuit160. As such, the power circuit 160 stores the backup power EE accordingto the auxiliary voltage VA in response to the control signal group CSG.

In an embodiment of the disclosure, the PWM signal generator 120 maydetect a voltage VS of the backup power EE. When the voltage VS of thebackup power EE is greater than or equal to the threshold voltage VT, itmeans that the power circuit 160 completes storage of the backup powerEE, and the PWM signal generator 120 thereby stops outputting thecontrol signal group CSG to the power circuit 160.

In an embodiment of the disclosure, the threshold voltage VT is aminimum voltage required by the PWM signal generator 120 for normaloperation, which should however not be construed as a limitation in thedisclosure.

FIG. 2 is a schematic block diagram of the power circuit 160 accordingto an embodiment of the disclosure. For ease of description, couplingrelationships between the power circuit 160 and the auxiliary winding Naand the PWM signal generator 120 and the energy storage element 140 arealso depicted in FIG. 2. With reference to FIG. 1 and FIG. 2 together,the power circuit 160 includes a charging circuit 262 and a power backupcircuit 264. The charging circuit 262 is coupled to the auxiliarywinding Na, the power terminal PVCC of the PWM signal generator 120, andthe energy storage element 140. The charging circuit 262 may rectify andfilter the auxiliary voltage VA to generate a first voltage V1, and maysupply power to the PWM signal generator 120 and charge the energystorage element 140 according to the first voltage V1.

The power backup circuit 264 is coupled to the charging circuit 262, thepower terminal PVCC of the PWM signal generator 120, and the energystorage element 140. When the voltage VCC of the energy storage element140 (i.e., the voltage of the power terminal PVCC of the PWM signalgenerator 120) is charged to be greater than or equal to the thresholdvoltage VT, the PWM signal generator 120 may output the control signalgroup CSG to the power backup circuit 264, so that the power backupcircuit 264 stores the backup power EE based on the first voltage V1. Inaddition, the PWM signal generator 120 may detect the voltage VS of thebackup power EE. When the voltage VS of the backup power EE is chargedto be greater than or equal to the threshold voltage VT, it means thatthe power backup circuit 264 is fully charged, and the PWM signalgenerator 120 thereby stops outputting the control signal group CSG tothe power backup circuit 264. Further, when the external power sourcestops supplying the input voltage VIN, the power backup circuit 264 maysupply power to the PWM signal generator 120 and charge the energystorage element 140 according to the backup power EE, and that the timefor powering the PWM signal generator 120 is extended.

FIG. 3 is a schematic diagram illustrating circuit architectures of thecharging circuit 262 and the power backup circuit 264 in the powercircuit 160 according to an embodiment of the disclosure. For ease ofdescription, the auxiliary winding Na, the PWM signal generator 120, andthe energy storage element 140 are also depicted in FIG. 3. Withreference to FIG. 1 and FIG. 3 together, the charging circuit 262includes a diode D21, a diode D22, and an auxiliary capacitor CAL Afirst terminal (i.e., a common-polarity terminal) of the auxiliarywinding Na is coupled to the ground terminal GND1. An anode terminal ofthe diode D21 is coupled to a second terminal (e.g., anopposite-polarity terminal) of the auxiliary winding Na to receive theauxiliary voltage VA. A cathode terminal of the diode D21 is coupled toa first node N1 and provides the first voltage V1. An anode terminal ofthe diode D22 is coupled to the first node N1. A cathode terminal of thediode D22 is coupled to the power terminal PVCC of the PWM signalgenerator 120 and the energy storage element 140. A first terminal ofthe auxiliary capacitor CA1 is coupled to the ground terminal GND1. Asecond terminal of the auxiliary capacitor CA1 is coupled to the firstnode N1.

The power backup circuit 264 may include an energy storage circuit 2641and a diode D41. The energy storage circuit 2641 is connected in seriesbetween the charging circuit 262 and the anode terminal of the diode D41and is configured to store the backup power EE. A cathode terminal ofthe diode D41 is coupled to the power terminal PVCC of the PWM signalgenerator 120 and the energy storage element 140.

In this embodiment, the control signal group CSG includes a controlsignal CS1. When the voltage VCC of the energy storage element 140 isgreater than or equal to the threshold voltage VT, the PWM signalgenerator 120 outputs the control signal CS1 to the energy storagecircuit 2641, and the energy storage circuit 2641 stores electricalenergy to serve as the backup power EE according to the first voltage V1in response to the control signal CS1. The PWM signal generator 120 maydetect a voltage VS1 of the electrical energy stored by the energystorage circuit 2641. When the voltage VS1 of the electrical energystored by the energy storage circuit 2641 is greater than or equal tothe threshold voltage VT, the PWM signal generator 120 may stopoutputting the control signal CS1 to the energy storage circuit 2641,and the energy storage circuit 2641 completes storage of the electricalenergy. In addition, when the external power source stops providing theinput voltage VIN, the energy storage circuit 2641 may supply power tothe PWM signal generator 120 and charge the energy storage element 140with the backup power EE through the diode D41.

Further, the energy storage circuit 2641 has an input terminal INT, acontrol terminal CT, and an output terminal OT. The input terminal INTof the energy storage circuit 2641 is coupled to the charging circuit262 to receive the first voltage V1. The output terminal OT of theenergy storage circuit 2641 is coupled to the anode terminal of thediode D41 and the PWM signal generator 120. The control terminal CT ofthe energy storage circuit 2641 receives the control signal CS1. In thisembodiment, the energy storage circuit 2641 includes a power switch Q2,a diode D42, and an energy storage capacitor CA2. A first terminal and acontrol terminal of the power switch Q2 respectively serve as the inputterminal INT and the control terminal CT of the energy storage circuit2641. An anode terminal of the diode D42 is coupled to a second terminalof the power switch Q2. A first terminal of the energy storage capacitorCA2 and a cathode terminal of the diode D42 are coupled to each other toserve as the output terminal OT of the energy storage circuit 2641. Asecond terminal of the energy storage capacitor CA2 is coupled to theground terminal GND1.

Operational details of the charging circuit 262 and the power backupcircuit 264 of FIG. 3 are described as follows. With reference to FIG. 1and FIG. 3 again, when the external power source starts providing theinput voltage VIN to the power conversion apparatus 100, the auxiliarywinding Na may charge the auxiliary capacitor CA1 through the diode D21and provide the first voltage V1 at the first node N1. Further, theauxiliary winding Na may charge the energy storage element 140 throughthe diodes D21 and D22.

The PWM signal generator 120 may detect the voltage VCC of the energystorage element 140 through the power terminal PVCC. When the PWM signalgenerator 120 detects that the voltage VCC of the energy storage element140 is charged to be greater than or equal to the threshold voltage VT,the PWM signal generator 120 may output the control signal CS1 having alogic high level to turn on the power switch Q2. As such, the auxiliarywinding Na starts charging the energy storage capacitor CA2 through thediodes D21 and D42 to serve as the backup power EE.

In addition, the PWM signal generator 120 may detect the voltage VS1 ofthe energy storage capacitor CA2 through the output terminal OT of theenergy storage circuit 2641. When the voltage VS1 of the energy storagecapacitor CA2 is greater than or equal to the threshold voltage VT, itmeans that the energy storage capacitor CA2 is fully charged and the PWMsignal generator 120 may thereby stop outputting the control signal CS1or may output the control signal CS1 having a logic low level to turnoff the power switch Q2.

From another perspective, when the external power source stops providingthe input voltage VIN, the auxiliary winding Na stops supplying power tothe PWM signal generator 120 and stops charging the energy storageelement 140, as such, the voltage VCC of the energy storage element 140drops. When a voltage difference between the voltage VS1 of the energystorage capacitor CA2 and the voltage VCC of the energy storage element140 is greater than a cut-in voltage of the diode D41 (i.e., a minimumvoltage required by the diode D41 to be turned on), the diode D41 isturned on. As such, the electrical energy stored by the energy storagecapacitor CA2 (i.e., the backup power EE) may be used to supply power tothe PWM signal generator 120 and charge the energy storage element 140.In this way, the time for powering the PWM signal generator 120 isprolonged, so that the hold-up time that the power conversion apparatus100 continuously supplies the output voltage VO is thereby extended.

Incidentally, the relationship between the logic high/low level of thecontrol signal CS1 and on/off of the power switch Q2 is provided toserve as an example only. People having ordinary skill in the art knowthat the relationship between the logic high/low level of the controlsignal CS1 and on/off of the power switch Q2 may be defined by adesigner according to practical needs.

FIG. 4 is a schematic diagram illustrating circuit architectures of acharging circuit 262 and a power backup circuit 464 in a power circuit160′ according to another embodiment of the disclosure. For ease ofdescription, the auxiliary winding Na, the PWM signal generator 120, andthe energy storage element 140 are also depicted in FIG. 4. Withreference to FIG. 1, FIG. 3, and FIG. 4 together, the charging circuit262 in FIG. 4 is similar to the charging circuit 262 in FIG. 3, sorelated description of FIG. 3 may be referred to, and repeateddescription is not provided herein.

In addition, compared to the power backup circuit 264 of FIG. 3 whichhas the diode D41 and one energy storage circuit 2641, the power backupcircuit 464 of FIG. 4 has the diode D41 and two energy storage circuits4641 and 4642. Specifically, the energy storage circuits 4641 and 4642are connected in series in sequence and are connected in series betweenthe charging circuit 262 and the anode terminal of the diode D41. Thecathode terminal of the diode D41 is coupled to the power terminal PVCCof the PWM signal generator 120 and the energy storage element 140.

In this embodiment, the control signal group CSG may include controlsignals CS1 and CS2. When the voltage VCC of the energy storage element140 is greater than or equal to the threshold voltage VT, the PWM signalgenerator 120 respectively outputs the control signals CS1 and CS2 tothe energy storage circuits 4641 and 4642. The energy storage circuits4641 and 4642 store electrical energy to serve as the backup power EEtogether according to the first voltage V1 in response to the controlsignals CS1 and CS2 respectively. The PWM signal generator 120 maydetect voltages VS1 and VS2 of the electrical energy stored by each ofthe energy storage circuits 4641 and 4642. When the voltage VS2 of theelectrical energy stored by the energy storage circuit 4642 is greaterthan or equal to the threshold voltage VT, the PWM signal generator 120may stop outputting the corresponding control signal CS2 to the energystorage circuit 4642, and the energy storage circuit 4642 completesstorage of the electrical energy. Similarly, when the voltage VS1 of theelectrical energy stored by the energy storage circuit 4641 is greaterthan or equal to the threshold voltage VT, the PWM signal generator 120stops outputting the corresponding control signal CS1 to the energystorage circuit 4641, and the energy storage circuit 4641 completesstorage of the electrical energy. In addition, when the external powersource stops providing the input voltage VIN, the energy storagecircuits 4641 and 4642 may supply power to the PWM signal generator 120and charge the energy storage element 140 with the backup power EEthrough the diode D41.

Further, each of the energy storage circuits 4641 and 4642 has the inputterminal INT, the control terminal CT, and the output terminal OT. Theinput terminal INT of the first energy storage circuit 4641 is coupledto the charging circuit 262 to receive the first voltage V1. The outputterminal OT of the first energy storage circuit 4641 is coupled to theinput terminal INT of the second energy storage circuit 4642 and the PWMsignal generator 120. The output terminal OT of the second energystorage circuit 4642 is coupled to the anode terminal of the diode D41and the PWM signal generator 120.

The control terminal CT of the energy storage circuit 4641 receives thecontrol signal CS1, and the control terminal CT of the energy storagecircuit 4642 receives the control signal CS2. In this embodiment, theenergy storage circuit 4641 includes a power switch Q21, a diode D421,and an energy storage capacitor CA21. A first terminal and a controlterminal of the power switch Q21 respectively serve as the inputterminal INT and the control terminal CT of the energy storage circuit4641. An anode terminal of the diode D421 is coupled to a secondterminal of the power switch Q21. A first terminal of the energy storagecapacitor CA21 and a cathode terminal of the diode D421 are coupled toeach other to serve as the output terminal OT of the energy storagecircuit 4641. A second terminal of the energy storage capacitor CA21 iscoupled to the ground terminal GND1. Similarly, the energy storagecircuit 4642 includes a power switch Q22, a diode D422, and an energystorage capacitor CA22. A first terminal and a control terminal of thepower switch Q22 respectively serve as the input terminal INT and thecontrol terminal CT of the energy storage circuit 4642. An anodeterminal of the diode D422 is coupled to a second terminal of the powerswitch Q22. A first terminal of the energy storage capacitor CA22 and acathode terminal of the diode D422 are coupled to each other to serve asthe output terminal OT of the energy storage circuit 4642. A secondterminal of the energy storage capacitor CA22 is coupled to the groundterminal GND1.

Operational details of the charging circuit 262 and the power backupcircuit 464 of FIG. 4 are described as follows. With reference to FIG. 1and FIG. 4, when the external power source starts providing the inputvoltage VIN to the power conversion apparatus 100, the auxiliary windingNa may charge the auxiliary capacitor CA1 through the diode D21 andprovide the first voltage V1 at the first node N1. Further, theauxiliary winding Na may charge the energy storage element 140 throughthe diodes D21 and D22.

The PWM signal generator 120 may detect the voltage VCC of the energystorage element 140 through the power terminal PVCC. When the PWM signalgenerator 120 detects that the voltage VCC of the energy storage element140 is charged to be greater than or equal to the threshold voltage VT,the PWM signal generator 120 may output the control signals CS1 and CS2having the logic high level to respectively turn on the power switchesQ21 and Q22. As such, the auxiliary winding Na starts charging theenergy storage capacitors CA21 and CA22 through the diodes D21, D421,and D422 to serve as the backup power EE together.

In addition, the PWM signal generator 120 may detect the voltage VS2 ofthe energy storage capacitor CA22 through the output terminal OT of theenergy storage circuit 4642. When the voltage VS2 of the energy storagecapacitor CA22 is greater than or equal to the threshold voltage VT, itmeans that the energy storage capacitor CA22 is fully charged, and thePWM signal generator 120 may thereby stop outputting the control signalCS2 or may output the control signal CS2 having the logic low level toturn off the power switch Q22. Similarly, the PWM signal generator 120may detect the voltage VS1 of the energy storage capacitor CA21 throughthe output terminal OT of the energy storage circuit 4641. When thevoltage VS1 of the energy storage capacitor CA21 is greater than orequal to the threshold voltage VT, it means that the energy storagecapacitor CA21 is fully charged, and the PWM signal generator 120 maythereby stop outputting the control signal CS1 or may output the controlsignal CS1 having the logic low level to turn off the power switch Q21.

From another perspective, when the external power source stops providingthe input voltage VIN, the auxiliary winding Na stops supplying power tothe PWM signal generator 120 and stops charging the energy storageelement 140, as such, the voltage VCC of the energy storage element 140drops. When a voltage difference between the voltage VS2 of the energystorage capacitor CA22 and the voltage VCC of the energy storage element140 is greater than the cut-in voltage of the diode D41, the diode D41is turned on. As such, the electrical energy stored by the energystorage capacitor CA22 may be used to supply power to the PWM signalgenerator 120 and charge the energy storage element 140. In addition,when a voltage difference between the voltage VS1 of the energy storagecapacitor CA21 and the voltage VS2 of the energy storage capacitor CA22is greater than a cut-in voltage of the diode D422, the PWM signalgenerator 120 may turn on the power switch Q22. As such, the energystorage capacitors CA21 and CA22 supply power to the PWM signalgenerator 120 and charge the energy storage element 140 together.

Note that FIG. 3 serves as an example illustrating the power backupcircuit 264 having the diode D41 and one energy storage circuit 641 andFIG. 4 serves as an example illustrating the power backup circuit 464having the diode D41 and two energy storage circuits 4641 and 4642, butthe disclosure does not intend to limit the number of the energy storagecircuit in the power backup circuit. In other embodiments of thedisclosure, the power backup circuit may include a diode and N energystorage circuit(s), where N may be any positive integer. The N energystorage circuit(s) is/are connected in series in sequence and is/areconnected in series between the charging circuit and the anode terminalof the diode of the power backup circuit. Implementation and operationaldetails related to the N energy storage circuit(s) may be deduced withreference to the related description of FIG. 3 and FIG. 4, and thereby,repeated description is not provided herein.

In view of the foregoing, the power conversion apparatus provided by theembodiments of the disclosure may supply power to the PWM signalgenerator according to the stored backup power when the power conversionapparatus is powered off, such that the hold-up time that the powerconversion apparatus continuously provides the output voltage isextended.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodimentswithout departing from the scope or spirit of the disclosure. In view ofthe foregoing, it is intended that the disclosure covers modificationsand variations provided that they fall within the scope of the followingclaims and their equivalents.

What is claimed is:
 1. A power conversion apparatus, comprising: atransformer, having a primary winding and an auxiliary winding, whereinthe primary winding is configured to receive an input voltage from anexternal power source, and the auxiliary winding is configured toprovide an auxiliary voltage; a first power switch, coupled to theprimary winding, and controlled by a pulse width modulation signal; apulse width modulation signal generator, coupled to the first powerswitch, and configured to generate the pulse width modulation signal tocontrol on and off of the first power switch; an energy storage element,coupled to a power terminal of the pulse width modulation signalgenerator; and a power circuit, coupled to the auxiliary winding, thepower terminal of the pulse width modulation signal generator, and theenergy storage element, and configured to supply power to the pulsewidth modulation signal generator and charge the energy storage elementaccording to the auxiliary voltage, wherein the pulse width modulationsignal generator makes the power circuit stores a backup power accordingto the auxiliary voltage only when the pulse width modulation signalgenerator detects that a voltage of the energy storage element isgreater than or equal to a threshold voltage, wherein the power circuitsupplies power to the pulse width modulation signal generator andcharges the energy storage element according to the backup power whenthe external power source stops providing the input voltage.
 2. Thepower conversion apparatus as claimed in claim 1, wherein the pulsewidth modulation signal generator detects the second voltage of theenergy storage element through the power terminal, wherein when thesecond voltage of the energy storage element is greater than or equal tothe threshold voltage, the pulse width modulation signal generatoroutputs a control signal group to the power circuit, and the powercircuit stores the backup power according to the auxiliary voltage inresponse to the control signal group.
 3. The power conversion apparatusas claimed in claim 2, wherein the pulse width modulation signalgenerator is further configured to detect a third voltage of the backuppower, wherein when the third voltage of the backup power is greaterthan or equal to the threshold voltage, the pulse width modulationsignal generator stops outputting the control signal group to the powercircuit, and the power circuit completes storage of the backup power. 4.The power conversion apparatus as claimed in claim 1, wherein thethreshold voltage is a minimum voltage required by the pulse widthmodulation signal generator for normal operation.
 5. The powerconversion apparatus as claimed in claim 1, wherein the power circuitcomprises: a charging circuit, coupled to the auxiliary winding, thepower terminal of the pulse width modulation signal generator, and theenergy storage element, configured to rectify and filter the auxiliaryvoltage to generate a first voltage, and supplying power to the pulsewidth modulation signal generator and charging the energy storageelement according to the first voltage; and a power backup circuit,coupled to the charging circuit, the power terminal of the pulse widthmodulation signal generator, and the energy storage element, wherein thepower backup circuit stores the backup power according to the firstvoltage when the voltage of the energy storage element is greater thanor equal to the threshold voltage, wherein the power backup circuitsupplies power to the pulse width modulation signal generator andcharges the energy storage element according to the backup power whenthe external power source stops providing the input voltage.
 6. Thepower conversion apparatus as claimed in claim 5, wherein a firstterminal of the auxiliary winding is coupled to a ground terminal, andthe charging circuit comprises: a first diode, an anode terminal of thefirst diode coupled to a second terminal of the auxiliary winding toreceive the auxiliary voltage, and a cathode terminal of the first diodecoupled to a first node and providing the first voltage; an auxiliarycapacitor, a first terminal of the auxiliary capacitor coupled to theground terminal, and a second terminal of the auxiliary capacitorcoupled to the first node; and a second diode, an anode terminal of thesecond diode coupled to the first node, and a cathode terminal of thesecond diode coupled to the power terminal of the pulse width modulationsignal generator and the energy storage element.
 7. The power conversionapparatus as claimed in claim 5, wherein the power backup circuitcomprises: a first diode, a cathode terminal of the first diode coupledto the power terminal of the pulse width modulation signal generator andthe energy storage element; and N energy storage circuits, the N energystorage circuits connected in series in sequence, and connected inseries between the charging circuit and an anode terminal of the firstdiode, wherein N is a positive integer, wherein when the voltage of theenergy storage element is greater than or equal to the thresholdvoltage, the pulse width modulation signal generator outputs N controlsignals to the N energy storage circuits respectively, and the N energystorage circuits store electrical energy according to the first voltageto together serve as the backup power in response to the N controlsignals respectively, wherein the N energy storage circuits supply powerto the pulse width modulation signal generator and charge the energystorage element with the backup power through the first diode when theexternal power source stops providing the input voltage.
 8. The powerconversion apparatus as claimed in claim 7, wherein: the pulse widthmodulation signal generator is further configured to detect a fourthvoltage of the electrical energy stored by each of the N energy storagecircuits, wherein when the fourth voltage of the electrical energystored by one of the N energy storage circuits is greater than or equalto the threshold voltage, the pulse width modulation signal generatorstops outputting a corresponding one of the N control signals to theenergy storage circuit, and the energy storage circuit completes storageof the electrical energy.
 9. The power conversion apparatus as claimedin claim 7, wherein: each energy storage circuit in the N energy storagecircuits has an input terminal, a control terminal, and an outputterminal, the input terminal of a first energy storage circuit in the Nenergy storage circuits is coupled to the charging circuit to receivethe first voltage, the output terminal of a M^(th) energy storagecircuit of the N energy storage circuits is coupled to the inputterminal of a (M+1)^(th) energy storage circuit of the N energy storagecircuits, the output terminal of an N^(th) energy storage circuit of theN energy storage circuits is coupled to the anode terminal of the firstdiode, and the control terminal of each energy storage circuit of the Nenergy storage circuits receives one of the N control signals, wherein Mis a positive integer less than N.
 10. The power conversion apparatus asclaimed in claim 9, wherein each energy storage circuit of the N energystorage circuits comprises: a second power switch, a first terminal anda control terminal of the second power switch respectively serve as theinput terminal and the control terminal of the energy storage circuit; asecond diode, an anode terminal of the second diode coupled to a secondterminal of the second power switch; and an energy storage capacitor, afirst terminal of the energy storage capacitor coupled to a cathodeterminal of the second diode to serve as the output terminal of theenergy storage circuit, and a second terminal of the energy storagecapacitor coupled to a ground terminal.